Biotinidase converts biotin, an essential water-soluble vitamin, into its bioavailable form. Biotinidase deficiency is a rare autosomal recessive disorder, with an estimated prevalence of approximately 1:60,000 neonates,1 causing multiple carboxylase deficiencies (for which biotin is a coenzyme) and leading to energy depletion, due to impaired catabolism of several branched chain amino acids, gluconeogenesis, and fatty acid synthesis.2 Neurologic involvement in biotinidase deficiency manifests in the first few years of life, with seizures, optic atrophy, and sensorineural hearing loss.3 Conventional MR imaging and MR spectroscopy features reflect the known pathophysiologic mechanisms in this deficiency. Prolonged T1 and T2 of the white matter may be explained by diffuse interstitial edema. The lactate peak on MR spectroscopy is related to the conversion to anaerobic metabolism.4,5

A previous description of a patient with biotinidase deficiency5 demonstrated markedly reduced diffusion in the brain stem, middle cerebellar peduncles, splenium of the corpus callosum, posterior limbs of the internal capsules, corona radiata, and parieto-occipital gray matter. In our patient, a different pattern was observed, with moderately reduced diffusion and increased fractional anisotropy in the perirolandic white matter and centra semiovalia. This could be due to accelerated myelination of those areas, induced by the repeated neuronal electric activity of the seizures, as was previously reported in children with Stürge-Weber syndrome6 and in experimental studies in mice.7 Vacuolating myelinopathy and myelin edema were previously described in neuropathologic studies in biotinidase deficiency.3 However, in our patient, these seem an unlikely explanation for the imaging findings because intramyelinic edema usually causes markedly reduced water diffusion and decreased fractional anisotropy in white matter.8